1. Field of the Invention
The present invention relates to a method for producing an optical transmitting member-holding structure in which one or more optical transmitting members such as optical fibers are held at a given location. The invention also relates to such an optical transmitting member-holding structure itself.
2. Related Art Statement
Various substrates for fixing plural optical fibers each having a diameter of for example, about 125 .mu.m are known. Ordinarily, a holding substrate is provided with fixing grooves, such as V-shaped grooves, for fling the optical fibers at given locations. After plural optical fibers, for example, sixteen optical fibers are fixed to the holding substrate, this substrate itself is fixed to another optical part. At that time, each optical fiber is coupled to, for example, a light-emitting diode or a light-receiving element, or optically coupled to another optical fiber or rod lens.
As a material for the holding substrate, silicon, optical glass, ceramics, etc. are known. Further, the above fixing grooves are formed by etching for the holding substrate made of silicon or by grinding for the glass or ceramic substrate.
In any type of the substrate, if the optical axis of the optical fiber fixed to the substrate is deviated from its given location, a transmission loss increases between the optical fiber and the other optical transmitting means. Therefore, an extremely high working precision, for example, not more than 0.5 .mu.m, is required as that in working the fixing groove on the optical fiber-holding substrate. The optical fibers are usually fixed in the V-shaped grooves with a resinous adhesive.
However, it is feared that if each optical fiber of such an optical transmitting member-holding structure is coupled to the light-emitting diode or the light-receiving element, an organic gas is generated from the resinous adhesive, is adhered to a light-emitting interface of the light-emitting diode, and deteriorates its light-emitting performance.
In order to avoid the occurrence of the above problem, the present inventors examined a technique for fixing each optical fiber into the corresponding V-shaped groove with solder. However, since the present optical fiber ordinarily has a diameter of about 125 .mu.m and a gap between the surface of the V-shaped groove and the optical fiber is very small, it turned to be difficult to flow the solder into the V-groove from a terminal end face of the holding substrate and fill it in the V-shaped groove with no void. Therefore, a void in which no solder flows is likely to be formed between the surface of the V-shaped groove and the optical fiber.
The behavior of such a void in the solder within the groove is not clear. The optical fiber-holding structure as referred above is often placed in a principal position in such a state that the holding structure is received in a gas-tight casing or package. Into the receiving casing or package is often charged an inert gas such as nitrogen gas so as to prevent degradation of the optical element such as laser. However, if the package is sealed with such an optical fiber-holding structure itself it was made clear that if the groove is not fully filled with the solder as mentioned above, a void is retained and such a void propagates along the groove over a large distance, the inert gas may leak out along the propagated void inside the groove.
The package as mentioned above in which the optical fiber-holding structure is received is often placed under severe outside environment, so that it may be exposed to a high temperature of 60.degree. C. to a low temperature of -40.degree. C. or may be exposed to desert environment to highly humid environment. Therefore, the package in which the optical fiber-holding structure is placed must operate stably under the above severe surrounding environment for a long time. However, if a void is retained in the solder within the groove as mentioned above, air remaining in the void is repeatedly expanded and shrunk or moisture may enter the void. This sometimes makes the fixing location of the optical fiber slightly change. If the fixing location of the optical fiber changes, its optical axis deviates even in the case that such a change is slight. Consequently, the coupling loss increases or changes.